Officials at the University of Maryland, College Park, want the Maryland Transit Administration to run its proposed Purple Line through a yet-to-be-built underground tunnel on campus, but planners insist an above-ground route along the campus' main road is still the project's only viable option.

MTA officials have long favored running the Purple Line  a proposed 16-mile, $1.5 billion light rail from New Carrollton to Bethesda  along Campus Drive, the university's most-trafficked road, to make it more accessible for students and staff. UM officials objected, saying the train could hit pedestrians and interfere with nearby research equipment.

The university now wants an underground route through campus, but state officials said at a Monday night public forum on campus that the route would drive up costs and endanger possible funding from the Federal Transit Administration.

The FTA could decide this summer or fall whether to fund the project's next step, a two-year preliminary engineering phase. The project's "absolute best-case scenario" is to break ground in 2013 and complete the project in 2016 or 2017, according to project planners.

"Without the federal funding, there's no project," said Del. Tom Hucker (D-Dist. 20) of Silver Spring. "We're not about to let a few overpaid leadership folks at the University of Maryland insist on a tunnel here and put the project in danger."

The MTA's proposed route would have stops at the College Park Metro station, East Campus, Campus Drive at UM's student union and West Campus near the University of Maryland, University College. The university's proposal would eliminate the Campus Drive stop and instead run an approximately 0.4-mile underground tunnel just south of UM's McKeldin Mall.

MTA officials say the tunnel could cost an additional $51 million, while the university projects a $42 million increase. The university is willing to raise the additional funds through private donors, said UM spokesman Millree Williams.

"We want the Purple Line on campus as badly as anyone else," Williams said. "We want to stay at the table with the MTA for as long as we need to, to get it resolved in a way that works for everyone."

Even if the university pays for the tunnel, the cost increase would still hurt the project's chances at federal funding, said Purple Line project manager Mike Madden, due to FTA criteria that look at total costs, regardless of funding sources.

"The Purple Line has to compete in a national arena with projects all over the country who are very limited about funds," Madden said. "Campus Drive is not only the best option, it's the only option."

Madden said the MTA has already made concessions for the university, such as giving the Purple Line a 15 mph speed limit on campus, and distributing electrical current along above- and below-ground trolley wires to decrease electromagnetic interference, or EMI.

He said active cancellation devices can also reduce EMI, but some professors at the university remain worried that the rail cars could still cause interference or prevent future science buildings from being built along the route.

"Most of the sensitive research buildings are on the northern part of campus [near Campus Drive]," said physics professor Steve Rolston. "Now we have the chance to pick an alignment that has less impact on research. ... It's still an issue, but it's not an impossible issue."

MTA officials are still gathering ridership data for the Purple Line, Madden said, and hope to reach an agreement with the university before submitting their proposal to the FTA this summer or fall.